Food habits of the river otter in a boreal ecosystem

Food habits of river otter (Lontra canadensis) were quantified by analysis of 1191 scats systematically collected in the Winefred Lake area (Athabasca River drainage) of northeastern Alberta to assess seasonal prey selection, the utility of scats for fish inventory, and the prominence of beavers as otter food. Fish dominated the annual diet, being found in 91.9% of scats. Insects, molluscs, crustaceans, and waterfowl were also substantial prey. Less agile, abundant shallow-water fish, such as a catostomid and various cyprinids, were the most common prey. Coregonine fish dominated the diet during their autumn spawning, were rarely eaten in summer when in the hypolimnion, but appeared to be preferred prey. In winter, with virtually no open water, the diet was less diverse and was dominated by cyprinid and gasterosteid fish. Such a fish fauna exists in small lakes, bog ponds, and beaver impoundments. We hypothesize that in winter, otters select water bodies, and consequently available prey, on the basis of shoreline substrate and morphology and relative ease of passage from air to water. Otter scats contained 14 of 18 fish species known to be in the study area. However, the contents of scats overestimated the diversity offish species inhabiting individual lakes. Beavers were occasionally eaten by otters, but were a minor component of the diet.